Flame safety electronic control



2,720,614 Patented Oct. 11, 1955 thee 18 Claims. (Cl. 317 123) The present invention relates to improved control circuits of the type useful in, for example but not necessarily limited to, arrangements whereby the operation of a main gas burner valve to open position may be effected only when the associated pilot flame is burning.

In general, the present invention contemplates the use of a saturable reactor having a control winding connected to a thermocouple disposed in or adjacent a pilot flame, the saturable reactor being tuned and connected in one arm of a balanced bridge circuit. The galvanometer arm of such bridge circuit includes the control grid and cathode of a gaseous discharge device such as a thyratron for controlling the firing of the same in accordance with the phase difference between an alternating voltage applied to its anode and the alternating voltage applied through said bridge circuit to the control grid.

One of the main objects of the present invention is to provide an improved control apparatus of this type in which a small continuous voltage generated by a thermocouple and, in the order of a few millivolts, may serve to operate the contacts of an associated relay, using relatively few and inexpensive circuit components.

Another object of the present invention is to provide an improved control apparatus of this character which incorporates a tunable saturable reactor to control the phase relationship of the voltages applied to the control grid and positive electrode of an associated discharge device to effect operation of a relay connected to such discharge device.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings in which:

Figure 1 is a partly schematic and partly structural representation of apparatus embodying features of the present invention.

Figure 2 shows in greater detail the manner in which the windings of the saturable reactor 3d are wound on a three-legged core structure.

It will be observed that while the present invention is illustrated as being embodied in a control for a pilot and associated main burner in a gas heating system, it is understood that certain aspects of the present invention may serve other uses and purposes than the ones described with particularity herein, and that the particular arrangement described specifically herein is merely illustrative of such other uses and purposes.

The arrangement shown in the drawing includes a pilot burner 10, a main burner 11 and a solenoid valve 12 arranged to control the fiow of gas to the main burner, the pilot being arranged to be ignited by a small igniter electrical glow coil 13 disposed adjacent thereto, and the gas in the main burner being ignited by the flame of the pilot burner. Further, the pilot burner 10 has associated therewith a thermocouple 14 heated thereby, either by being immersed in the pilot burner flame or by radiation from such pilot flame.

The energization of the solenoid valve 12, on the one hand, and the igniter glow coil 13, on the other hand, is controlled by the single pole double throw switch 15 comprisin the two stationary contacts 15A, 15B and movable contact 15C of the relay 16 having the control winding 16A. The relay winding 16A is connected in the anode-cathode circuit of the discharge device 17 to effect operation of the switch 15 in accordance with the phase relationship between the alternating current voltages applied, on the one hand, to the anode 18 of the device 17, and on the other hand, to the control grid The anode 18 is connected through relay winding to one terminal of secondary winding 22A which has its other terminal connected to the cathode 37.

' 'ietly, as described more in detail hereinafter, when t mocouple 14 is heated suliiciently by the flame pilot burner 16, the movable contact 15C engages cnary contact 158, as shown in the drawings, t energization of the winding of the solenoid lve to open such normally closed valve through a circuit which comprises the switch 15B, 15C, the

g of the solenoid valve 12, a switch in the thermo- 2b', a switch in the limit control 21 and the low voltage secondary winding 22 of the transformer 23 which has its primary winding 24 connected to and energized by the alternating current voltage source 25.

On the other hand, the igniter glow coil 13 is connected in a serial circuit which comprises such coil 13, the switch 15A, 15C, normally closed by tension spring iii), the secondary winding 22 and a switch in the manually operable control 27 designated in the drawing as a n -r1ual reset thermal cut-off.

h control 27 is of conventional structure and, per arms no part of the present invention, although it rstood that controls of this type include a manually operated switch which remains closed for a predetermined time interval after manual actuation of a control desigated as push button 27A, and also with such conroi 27 including thermally operated means whereby such .ianually operated switch is returned to its normal open 1 osition after such predetermined time interval. Thus, o initially ignite the pilot burner 19, the push button 7"- is actuated to cause the glow coil 13 to glow .nu ignite the gas flowing from burner 10, it being oted that at this stage of operation the switch 15A, 5C is in its normally closed position to allow heating curr at to flow to coil 13.

A indicated above, the operation of the relay switch e ncnt 3.56 from its normal position engaging contact a to its position shown in the drawings where it ene the switch contact 15B is effected by changing the s p ase relationship of the alternating current voltage applieon the one hand, to the anode 18, and on the other hand, to the control grid 19. More specifically,

the operation of the relay i6 is effected by controlling the phase of the alternating curent voltage applied to the control grid 19, such alternating current voltage appearing at the control grid 19 being effected by the tuned condition of the saturable reactor 38 which is connected in a bridge circuit having the general reference numeral 31. This bridge circuit 31 has in the first arm thereof: the resistance 33; in the second arm thereof: the saturable reactor 39 shunted by the tuning condenser 34; and the third and fourth arms thereof comprise, respectively: the windings 35A and 358 which lie on opposite ends of a center tap 35C on the secondary transformer winding 35.

it is observed that the grid 19 is connected through the shunt connected grid leak-grid condenser combination 36, 36A to the junction point 60 of the condenser 34 and resistance 33, while the center tap 350 is connected to the cathode 37. The condenser resistor combination 36 and 36A is used to establish a negative bias on the tube to keep it in a non-operating condition. This bias is derived by rectifier action between the grid and cathode.

The condenser 38 connected directly between the grid and cathode serves to establish the time constant of the grid-cathode circuit of the tube to a value preferably less than one-tenth of a second, whereby a desired time delay is introduced whereby the discharge device 17, a gaseous type of tube, for example, a Thyratron, is rendered substantially insensitive to transient voltages such as those resulting from fluctuations in the line voltage applied to the primary winding 24 of the transformer 23. For the same purpose, a condenser 41') is connected across the terminals of the relay winding 16A to prevent spurious operation of the relay resulting from fluctuations in line voltage. The eifects thus contributed by the grid condenser 38 and relay condenser 40 thus stabilize the operation of the circuit and avoid spurious firing of the tube 17 which might otherwise be initiated in accordance with fluctuations in the voltage source 25.

The saturable reactor 30 may comprise a three-legged magnetic core structure, as shown in Figure 2, with opposed windings 39A and 30B on the outside legs, namely, the first and third legs, while a low impedance winding 30C connected to the thermocouple 14 is wound around the intermediate or second leg. Since the two outside windings 30A, 30B are connected in opposed relationship, it is clear that the magnetic flux produced by the continuous current flowing in the control winding 36C produces an additive effect with respect to the flux produced by one of the coils 39A and a subtractive eflect with respect to the flux produced by the other coil 393. In other words, assuming that the flux produced by the outside windings 30A, 303 have their instantaneous directions represented respectively by the arrows 56 and 51, and the flux produced by the control winding 3iiC and passing from the central leg 54 to the outside legs 52 and 53 have their directions represented respectively by the arrows 56 and 57, it is clear that the fluxes passing through leg 52 and represented by the arrows 50 and 56 are in opposition, whereas the fluxes passing through the outside leg 53 and represented by the arrows 51 and 57 are in additive relationship. Further, it is observed that the fluxes produced by windings 39A and 3GB aid each other in the outside legs 2 and 53 of the core structure but oppose each other in the center leg 54.

The eflect of an increase in continuous current through the center control winding 30C causes the net inductance of the saturable reactor to decrease. Thus, when the pilot burner 10 is lit the pilot flame causes suflicient current to flow from the thermocouple 14 through the control winding 30C to decrease the inductance of the saturable reactor to such an extent that the parallel circuit 39, 34 comprising the saturable reactor 30 and condenser 34, which may be in the order or" .05 microfarad, is tuned to the frequency of the supply voltage E5, namely, 60 cycles. It is thus observed that when the flame of the pilot is extinguished, the net inductance of the saturable reactor increases and the parallel circuit, comprising the reactor and condenser, is detuned and no longer resonant at 60 cycles.

It is, of course, well known that a parallel tuned circuit, at its resonant frequency, may be represented by a resistance. In this case the effective resistance of the tuned circuit 30, 34 is equal to the magnitude of the resistance 33 in the opposite arm of the bridge previously described, thereby establishing a balanced condition when the pilot flame burns. In this balanced condition the potential and phase of the junction point 64 i. e. between condenser 34 and resistance 33 is at substantially the same potential and phase as center tap 35, i. e., the potential and phase of cathode 37, thereby establishing the potential and phase of grid 19 at substantially the same potential and phase as the cathode 37 or slightly positive with respect to the cathode due to grid current flowing through resistance 36. In this balanced condition the tube 17 is in optimum condition for firing, i. e., for sustained flow of large anode currents through the relay winding 16A to maintain the relay contact 15C in the position shown in Figure 1, since the grid 19 and anode 18 are substantially in phase.

It is desirable that the ratio of inductance to capacity in the parallel circuit 30, 34 be of high magnitude and yet the effective resistance of such circuit should be as small as possible. In other words, it is desirable that the Q, i. e., the so-called quality factor of the tuned circuit 39, 34 at the resonant frequency be as high as practically possible, so that the voltage applied to the grid 19 may be altered to a relatively large extent upon a relatively slight change in the inductance of the reactor 30.

It is well understood that the phase shift between the current and voltage in a parallel resonant circuit changes most rapidly when and as such circuit is being detuned from its resonant condition either in the direction where such circuit may be represented by a capacitive reactance or in a direction where such circuit may be represented by an inductive reactance; and it is this principle which is utilized in effecting a sensitive control whereby the phase of the voltage applied to the grid 37 may be altered over a considerable range by an accompanying small change in current flow through the control winding 30C.

Thus, when the pilot light 10 is extinguished, for any reason whatsoever, the current through thermocouple 14 diminishes to cause unbalancing of the bridge 31 and a resulting change in phase between the voltage, on the one hand, at center tap 35C and, on the other hand, at junction point 60, to such an extent that the phase of the voltage appearing on grid 19 is sufficiently out of phase with respect to the voltage on anode 18, that the tube 17 ceases to conduct, whereupon, the relay 16 is deenergized, the switch 15C, 158 is allowed to open under the influence of tension spring 15D to deenergize the solenoid valve 12, to thereby prevent the flow of gas to the main burner 11. At the same time, the movable switch contact 15C engages the stationary relay contact 15A to condition the pilot lighting circuit including glow coil 13 for subsequent energization, such energization being accomplished by actuating the push button 27A whereupon the gas issuing from the pilot 10 may be ignited.

While the particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. In apparatus of the character described, the combination comprising an electron discharge device having an output electrode, a control grid and a cathode, an alternating current voltage source, circuit means connecting said source between said output electrode and said cathode for the flow of space current through said device, second circuit means connecting said source be tween said control grid and said cathode, said second circuit means including a bridge circuit having a saturable reactor in one arm thereof, a thermocouple for heating by a flame, the direct current control winding of said reactor being connected to said thermocouple and operative upon energization of said thermocouple to produce a direct current flux in said reactor to tune said reactor to the frequency of said source to thereby alter the phase relationship between the voltage applied to said output electrode, on the one hand, and to said control grid on the other hand to thereby change the intensity of said space current, a utilization device and space current responsive means for controlling said utilization device.

2. In apparatus of the character described, the combination comprising an electron discharge device having an output electrode, a control grid and a cathode, an alternating current voltage source, first circuit means connecting said source to said output electrode and said cathode for producing a flow of space current through said device, second circuit means connecting said source between said control grid and said cathode, said second circuit means including a bridge circuit having a saturable reactor in one arm thereof, a thermocouple heated by a flame, said thermocouple being connected to said reactor to balance said bridge circuit to thereby alter the phase of the alternating voltage applied to said grid with respect to the phase of the voltage on said output electrode to thereby change the intensity of said space current, a utilization device and space current responsive means for controlling said utilization device.

3. In apparatus of the character described, the combination comprising a thermocouple heated by a flame, a utilization device, an electron discharge device includ ing a control grid and an output electrode for energizing said utilization device, an alternating current voltage source, circuit means applying a voltage derived from said source to said output electrode, second circuit means applying a second voltage derived from said source to said control grid, said second circuit means including a bridge circuit having a saturable reactor in one arm thereof with a continuous current control winding thereon, said thermocouple being connected to said control winding and effective to tune said reactor to the frequency of said source when said thermocouple is heated by said flame thereby altering the phase relationship between the voltage applied to said output electrode with respect to the voltage applied to said control grid to thereby alter the space current flowing to said output electrode, and space current responsive means for controlling said utilization device.

4. In apparatus of the character described, the combination comprising a thermocouple heated by a flame, a utilization device, an electron discharge device operative to energize said utilization device, said discharge device including an output electrode and a control grid, a transformer, means including a first secondary winding of said transformer for applying an alternating current voltage to said output electrode, means including a second secondary winding of said transformer for applying an alternating current voltage to said control grid, said last mentioned means including a bridge circuit connected between the control grid and cathode of said discharge device, said bridge circuit including in a first arm thereof the alternating current winding of a saturable reactor having a control winding, said control winding being connected to said thermocouple, an impedance, said bridge circuit having said impedance in a second arm thereof, said second arm being disposed in shunt with respect to said first arm, the third and fourth arms of said bridge circuit comprising respectively halves of said second secondary winding, the center point on said second secondary winding being connected to said cathode, the junction point of said saturable reactor and said resistance being connected to said control grid, and means tuning the alternating current winding of said saturable reactor to resonance with the frequency of said alternating current voltage when said thermocouple is heated, and said utilization device being actuated in accordance with space current flowing to said output electrode.

5. In apparatus of the character described, the combination comprising a thermocouple heated by a flame, a utilization device, an electron discharge device having a control grid and an output electrode connected to said utilization device and operating the same, means applying alternating voltages to said output electrode and said control grid, means altering the phase relationship of said alternating voltages applied to said output electrode and said control grid in accordance with the voltage generated by said thermocouple to thereby alter the space current flowing from said electrode, the last mentioned means comprising a saturable reactor connected between the control grid and cathode of said device, said saturable reactor having mounted thereon a control winding connected to said thermocouple and serving when heated by said flame to tune said reactor to the frequency of the energizing source.

6. In apparatus of the character described, the combination comprising a saturable reactor having an alternating current winding and a continuous current winding, a thermocouple heated by a flame, said thermocouple having opposite terminals thereof connected to opposite terminals of said continuous current winding to effect inductance changes in the alternating current winding of said saturable reactor, condenser means connected in shunt with said alternating current winding and effective to tune said reactor to the frequency of the supply voltage when the thermocouple is heated, a transformer having a center tapped secondary winding, an electron discharge device having a cathode, a control grid and an anode, the center tap on said secondary winding being connected to said cathode, an impedance, said secondary winding being connected in a bridge circuit, said bridge circuit having the shunt connected condenser means and alternating current winding in one arm thereof, said impedance in a second arm thereof, and the two halves of said center tapped winding in third and fourth arms thereof, a shunt connected grid leak-condenser combination, said grid being connected to the junction point of said condenser means with said impedance through said grid leak-condenser combination, a second secondary winding on said transformer having one terminal thereof connected to said cathode, a relay winding having one of its terminals connected to said anode and the other one of its terminals connected to the other terminal of said second secondary winding, a utilzation device, said relay winding have associated therewith a normally open switch, and means effective to energize said utilization device through said normally open switch.

7. The arrangement set forth in claim 6 in which a first stabilizing condenser is connected between said control grid and said cathode, and a second stabilizing circuit is connected in shunt with said relay winding.

8. The arrangement set forth in claim 6 in which said relay winding has associated therewith a normally closed switch actuated thereby, a glow coil adjacent said flame, a voltage source, and manual control means connecting said source to said glow coil.

9. The arrangement set forth in claim 6 in which said saturable reactor comprises a core structure having a pair of outside legs and a center leg, said center leg having said continuous current winding wound thereon, said out side legs having serially connected alternating current windings thereon which collectively comprise the aforesaid alternating current winding, continuous current from said thermocouple through said control winding being eflective to increase the net flux in one of said outside legs while decreasing the net flux in the other outside leg.

it). In apparatus of the character described, the combination comprising a saturable reactor having an alternating current Winding and a continuous current winding, a thermocouple heated by a flame, said thermocouple having opposite terminals thereof connected to opposite terminals of said continuous current winding to effect inductance changes in the alternating current winding of said saturable reactor, condenser means connected in shunt with said alternating current winding and effective to tune said reactor to the frequency of the supply voltage when the thermocouple is heated, a transformer having a center tapped secondary winding, an electron discharge device having a cathode, a control grid and an anode, the center tap on said secondarywinding being connected to said cathode, an impedance, said secondary winding being connected in a bridge circuit, said bridge circuit having the shunt connected condenser means and alternating current winding in one arm thereof, said impedance in a second arm thereof, and the two halves of said center tapped winding in third and fourth arms thereof, said grid being connected to the junction point of said condenser means and said impedance, a second secondary winding on said transformer having one terminal thereof connected to said cathode, a relay winding having one of its terminals connected to said anode and the other one of its terminals connected to the other terminal of said second secondary winding, a utilization device, said utilization device incorporating a solenoid, said relay winding having associated therewith a normally open switch, and means effective to energize said solenoid through said normally open switch.

11. In apparatus of the character described, the combination comprising a saturable reactor having an alternating current winding and a continuous current winding, a thermocouple heated by a flame, said thermocouple having opposite terminals thereof connected to opposite terminals of said continuous current winding to effect inductance changes in the alternating current winding of said saturable reactor, condenser means connected in shunt with said alternating current winding and effective to tune said reactor to the frequency of the supply voltage when the thermocouple is heated, a transformer having a center tapped secondary winding, an electron discharge device having a cathode, a control grid and an anode, the center tap on said secondary winding, an electron discharge device having a cathode, a control grid and an anode, the center tap on said secondary winding being connected to said cathode, an impedance, said secondary winding being connected in a bridge circuit, said bridge circuit having the shunt connected condenser means and alternating current winding in one arm thereof, said impedance in a second arm thereof, and the two halves of said center tapped winding in third and fourth arms thereof, said grid being connected to the junction point of said condenser means and said impedance, a second secondary winding on said transformer having one terminal thereof connected to said cathode, space current responsive means having one of its terminals connected to said anode and the other one of its terminals connected to the other terminal of said second secondary winding, and a utilization device actuated by said space current responsive means.

12. In apparatus of the character described, the combination comprising a saturable reactor having an alternating current winding and a continuous current winding, a thermocouple heated by a flame, said thermocouple having opposite terminals thereof connected to opposite terminals of said continuous current winding to effect inductance changes in the alternating current winding of said saturable reactor, condenser means connected in shunt with said alternating current Winding and effective to tune said reactor to the frequency of the supply voltage when the thermocouple is heated, a transformer having a center tapped secondary winding, an electron discharge device having a cathode, a control grid and an anode, the center tap on said secondary winding being connected to said cathode, said secondary winding being connected in a bridge circuit, said bridge circuit having the shunt connected condenser means and alternating current winding in one arm thereof, the terminals of the galvanometer arm of said bridge circuit, being connected respectively to said cathode and said control grid, a second secondary winding on said transformer having one terminal thereof connected to said cathode, space current responsive means having one of its terminals connected to said anode and the other one of its terminals connected to the other terminal of said second secondary winding and a utilization device actuated by said space current responsive means.

13. The arrangement set forth in claim 12 in which said saturable reactor comprises a core structure having a pair of outside legs and a center leg, said center leg having said continuous current winding wound thereon, said outside legs having serially connected alternating current windings thereon which collectively comprise the aforesaid alternating current winding, continuous current from said thermocouple through said control winding being effective to increase the net flux in one of said outside legs while decreasing the net flux in the other outside leg.

14. In apparatus of the character described, the combination comprising a thermocouple for heating by a flame, an electron discharge device having an output electrode and a control grid, means for energizing said electrode and control grid with an alternating current voltage, said discharge device having a cathode, a bridge circuit, the grid and cathode of said device being connected in the so-called galvanometer arm of said bridge circuit, one arm of said bridge circuit comprising a saturable reactor, and a condenser connected in shunt with said saturable reactor and serving to tune said saturable reactor to the frequency of said alternating current voltage when said thermocouple is heated by said flame.

15. In apparatus of the character described, the combination comprising a thermocouple for heating by a flame, an electron discharge device having an output electrode, a control grid and a cathode, first circuit means for connecting a source of alternating current voltage between said output electrode and said cathode for producing a flow of space current through said device, second circuit means for connecting said source between said control grid and said cathode, said second circuit means comprising a bridge circuit, one arm of said bridge circuit comprising a saturable reactor, a second arm of said bridge comprising a resistance, and third and fourth arms of said bridge comprising a center tapped winding of a transformer for connection to said source, said saturable reactor having a control grid, said thermocouple being connected to said control winding, a condenser connected in shunt with said saturable reactor and serving, when said thermocouple is heated by said flame to tune said saturable reactor to the frequency of said source whereby the effective impedance of said saturable reactor with the condenser connected in shunt therewith with a resistance which has a magnitude substantially equal to the magnitude of the aforementioned resistance, and the cathode and control grid of said device being connected in the so-called galvanometer arm of said bridge circuit.

16. In an arrangement of the character described, the combination comprising a thermocouple for heating by a flame, an electron discharge device having an output electrode, a control electrode and a cathode, a first transformer winding connected between said cathode and said output electrode, a second transformer winding which is center tapped, the center tap on said lastmentioned winding being connected to said cathode, and comprising first and second arms of a bridge circuit, a saturable reactor comprising a third arm of said bridge circuit, an impedance comprising a fourth arm of said bridge circuit, said saturable reactor and said impedance having a common junction point, a grid leak resistance, a grid leak condenser connected in shunt with said grid leak resistance and having one of its terminals connected to said control electrode and the other one of its terminals connected to said junction point, and a control winding on said saturable reactor connected to said thermocouple.

17. The arrangement set forth in claim 16 including a condenser connected in shunt with said saturable reactor and serving to tune said saturable reactor, when said thermocouple is heated by said flame, to the frequency of the voltage applied to said transformer windings.

18. The arrangement set forth in claim 17 in which said impedance comprises a resistance which has a magnitude substantially equal to the effective resistance of the 9 reactor when tuned in accordance with said condenser and the heating of said thermocouple.

References Cited in the file of this patent UNITED STATES PATENTS 5 Bedford Mar. 7, 1933 Gauger July 9, 1935 Kerr June 29, 1937 Kuempel Dec. 27, 1938 Gutzmann Feb. 13, 1940 10 10 Laing Dec. 24, 1940 Sparrow Jan. 14, 1941 Ackerman Aug. 24, 1943 Rodgers Nov. 2, 1943 Yates Oct. 17, 1944 Paille Sept. 25, 1945 Carpenter Aug. 8, 1950 FOREIGN PATENTS Great Britain Feb. 10, 1949 

